In the early 1970's a significant improvement over the then conventional shot peening process (wherein spheroidal particles are blown at high velocity against a surface to be treated) was introduced by Winter et. al., and embodied in the roto peening devices such as those disclosed in U.S. Pat. Nos. 3,638,464 and 3,834,200. Both of these patents are assigned to the assignee of the present application and are incorporated herein by reference where necessary to understand the present invention. The latter patent discloses a high-intensity peening flap construction which includes an elongate strap of a flexible, tear-resistant material, and at least one metal peening particle support base fastened to the elongate strap. A plurality of refractory-hard, impact fracture-resistant peening particles are metallurgically joined to an exposed face of the support base. In use, one or more of the flaps are mounted on a hub, and the hub is rotated while the flaps are forced against the workpiece to be peened. The peening particles on each support base strike the workpiece in turn, thereby causing the peening particles to perform their normal peening function, but preventing the normal uncontrolled scattering which occurs in conventional shot peening. FIG. 1, discussed in more detail hereinbelow, shows a later version of the flap/hub construction, such as currently marketed by assignee, and shown in assignee's technical bulletin no 61-5000-5490-4(1282)II, published December, 1988.
Winter et. al. found that by inclining the peening faces of the support bases to the length of the strap in the static condition required less deformation of the strap to cause impact of the peening particles normal to the surface being peened. While this configuration significantly reduces wear on the strap material immediately around the support bases, in particularly harsh (abrasive) operating conditions, for example where the workpiece itself is abrasive, the flaps fail. Adjacent flaps tend to impact each other when one flap is impinging on the workpiece, especially when many flaps are used on one wheel, where the flap immediately trailing the impinging flap is unhindered in it forward motion. Hence, the strap material suffers less than optimal life due to self-impact. Where the peening action generates particles of workpiece material, the particles can contribute to strap wear by being sandwiched momentarily between adjacent flaps.
Devices such as those discussed herein above have used as the flap material a polyurethane impregnated nylon scrim, for example, the polyester polyurethane coated nylon fabric sold under the trade name "Reevecoat 7625" available from Reeves Brothers, Inc., with offices at New York, NY. Effective though it is for many purposes, the polyester polyurethane impregnated nylon scrim material exhibits poor flex fatigue characteristics and insufficient abrasion resistance. Thus, an unmet need exists for a high-intensity peening flap construction which can withstand harsh operating conditions and provide improved abrasion resistance (longer useful life) over previously known constructions.
Polycarbonate-polyether polyurethanes are known in the polymer coating industry. One polycarbonate-polyether polyurethane is sold under the trade name "Morthane CA-1225" (Morton International) and comprises the reaction product of a mixture of polycarbonate polyol and polyether polyols; a diisocyanate compound; and first and second extenders. U.S. Pat. No. 5,001,208 provides a more detailed description of these polyurethanes and their method of manufacture, and is expressly incorporated herein by reference thereto Linear polyurethane elastomers made using polycarbonate-polyether polyurethanes are also disclosed. However, neither the polycarbonate-polyether polyurethanes of U.S. Pat. No. 5,001,208, nor the linear polyurethane elastomers made therefrom have been suggested for use in high-intensity roto peening operations or devices.